Hemplime
The application of Hemplime (a mixture of hemp shives and lime) is promising as a carbon negative building material. Although the production of lime is carbon positive, the amount of lime used in this material is minimal compared to the amount of hemp. Hemp is a fast growing crop which does not need any furtilasion of the soil. There are many experimental projects in Hemplime and it is a steep learning curve. a few important lessons:
Hemplime is not structural. It can form a rather robust panel but it cannot carry any structural loading. The current application of hemplime relies on different materials for structure like timber.
Lime is brittle. As hemp is a plant based material it will shrink when dying out. Because hemplime relies on lime as a binder it is susceptible to cracking. Detailing of a building component has to allow for movement to prevent this.
Building structures will move because of settlements, creep, or dynamic loads. it is better to interrupt the hemplime where movement can be expected: for instance the roof / wall.
Hemp Lime is hydroscopic: it needs to be able to dry after it got wet. It should be kept away from the damp ground and cannot function as a roof surface. It is advisable to shield it from heavy rain by a cantilevering roof.
Hemplime is not airtight. A very thick wall can be nearly air tight but an additional coat of render or plaster is advisable to prevent air under pressure (high wind situations) traveling through the wall build-up.
